Novel Gemini Surfactant for Binding Eu(III)-Polyoxometalate into Hydrogels and Polymer Latexes

The incorporation of rare-earth ions into polymer matrices can lead to useful materials in various fields such as biomarkers, lasers, luminescent devices, optical storage materials, and so on. Methods of incorporation are either extremely simple, such as mixing the polymer and the ion of interest in adequate solvents, or more sophisticated such as synthesizing predesigned monomers that contain the rare-earth ion or binding the ion on an already formed polymer chain. Cationic gemini surfactants represent a class of surfactants that can be used to incorporate metal-oxygen cluster compounds by means of strong electrostatic interactions. In this study, first, a novel cationic gemini surfactant having double bonds on both side chains was designed and prepared. After characterization, the surfactant was used to synthesize hydrogels with different degrees of crosslinking and also as a surfmer in emulsion polymerization of methyl methacrylate. The resulted polymer matrices were able to bind europium-polyoxometalate Na₉[EuW₁₀O₃₆]^.32H₂O. In case of luminescent lanthanide ions, changing the microenvironment around the metal ion also changes the intensity of some emission peaks as well as other luminescent parameters. Investigation of emission spectra of Eu³⁺ indicates a decrease in the symmetry of the microenvironment, when the polyanions pass from water to latex, to surfactant solution, and to hydrogel.

The effect of hydration on the stability of ionic liquid crystals: MD simulations of [C14C1im]Cl and [C14C1im]Cl·H2O

The thermal range of the stability of Ionic Liquid Crystal (ILC) phases of imidazolium ILCs, and the type of the mesophase itself are affected by several molecular structural features, the two prominent ones being the alkyl chain length and the counter-anion. Hydration is also very important: monohydrate samples of 1-alkyl-3-methylimidazolium halides have a higher clearing point and a wider thermal range of the stability of the ionic smectic phase, compared with the analogous anhydrous sample. To understand the reasons, at a microscopic level, for such increased stability due to hydration, we run classical Molecular Dynamics (MD) simulations of a typical ionic liquid crystal, 1-tetradecyl-3-methylimidazolium chloride, and of its monohydrate form. We tested a full-charge non-polarizable force field and a scaled-charge version having the total charge of the ions scaled by a factor of 0.80. Comparison of the structural and dynamic properties with available experimental data reveals that the scaling of the charge by a factor of 0.80 results in a good agreement between simulated and experimental data and it sheds light on the microscopic mechanism responsible for the increased stability of the monohydrated phase. A hydrogen-bond network between water and the chloride anion is established in the ionic layer which increases the stability of the ionic layer; this in turn increases the nano-segregation between the ionic and hydrophobic layers which eventually produce an increased order of the alkylic layer as well.

Ion conformation and orientational order in a dicationic ionic liquid crystal studied by solid-state nuclear magnetic resonance spectroscopy

Ionic liquids crystals belong to a special class of ionic liquids that exhibit thermotropic liquid-crystalline behavior. Recently, dicationic ionic liquid crystals have been reported with a cation containing two single-charged ions covalently linked by a spacer. In ionic liquid crystals, electrostatic and hydrogen bonding interactions in ionic sublayer and van der Waals interaction in hydrophobic domains are the main forces contributing to the mesophase stabilization and determining the molecular orientational order and conformation. How these properties in dicationic materials are compared to those in conventional monocationic analogs? We address this question using a combination of advanced NMR methods and DFT analysis. Dicationic salt 3,3′-(1,6-hexanediyl)bis(1-dodecylimidazolium)dibromide was studied. Local bond order parameters of flexible alkyl side chains, linker chain, and alignment of rigid polar groups were analyzed. The dynamic spacer effectively “decouples” the motion of two ionic moieties. Hence, local order and alignment in dicationic mesophase were similar to those in analogous single-chain monocationic salts. Bond order parameters in the side chains in the dicationic smectic phase were found consistently lower compared to double-chain monocationic analogs, suggesting decreasing contribution of van der Waals forces. Overall dication reorientation in the smectic phase was characterized by low values of orientational order parameter S. With increased interaction energy in the polar domain the layered structure is stabilized despite less ordered dications. The results emphasized the trends in the orientational order in ionic liquid crystals and contributed to a better understanding of interparticle interactions driving smectic assembly in this and analogous ionic mesogens.

Stabilising disproportionation of lipophilic ionic liquid salts in lipid-based formulations

Lipid based formulations (LBFs) can enhance oral bioavailability, however, their utility may be restricted by low drug loading in the formulation. Converting drugs to drug-ionic liquids (drug-ILs) or lipophilic salts can significantly increase lipid solubility but this approach is complicated in some cases by salt disproportionation, leading to a reduction in solubility and physical instability. Here we explore the physical stability of the weakly basic model drug, cinnarizine (CIN), when paired with a decanoate counterion (Dec) to form the drug-IL, cinnarizine decanoate (CIN.Dec). Consistent with published studies of salt disproportionation in aqueous solution, weakly acidic counterions such as Dec lead to the generation of drug-IL lipid solutions with pHs below pH_max. This leads to CIN deprotonation to the less soluble free base and precipitation. Subsequent studies however, show that these effects can be reversed by acidification of the formulation (either with excess decanoic acid or other lipid soluble acids), stimulating a pH shift to the salt plateau of CIN.Dec and the formation of stable lipid solutions of CIN.Dec. Altering formulation pH to more acidic conditions, therefore stabilises drug-ILs formed using weakly acidic lipophilic counterions, and is a viable method to promote formulation stability via inhibition of disproportionation of some drug-ILs.

Dielectric properties of a bisimidazolium salt with dodecyl sulfate anion doped with carbon nanotubes

A new bisimidazolium salt with dodecyl sulfate as counterion has been designed and prepared. This salt shows a SmA phase that is stable at room temperature. The new ionic liquid crystal (ILC) was characterized by ¹H NMR, ¹³C NMR and IR spectroscopy. Its liquid crystalline properties were analyzed by polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray diffraction (XRD) studies. The dielectric spectra of the ILC doped with different concentrations of carbon nanotubes (CNT) were recorded over a wide frequency and temperature range of 10^-1 to 10⁷ Hz and 293-338 K, respectively. The values of the activation energy were found in the range of 0.46-0.61 eV; the characteristic time was obtained by fitting the spectra of the dielectric loss with the Havriliak-Negami functions. As a result of doping the ILC with CNT, the electric conductivity increases significantly. Ionic conductivity is dominant and it was indirectly observed through the electrode polarization (EP) effect. The very high dielectric permittivity values and the decrease of the electric conductivity at low frequencies confirm the presence of EP.